Heat Sink Fan and Method for Manufacturing Heat Sink That Is Used For the Heat Sink Fan

ABSTRACT

A heat sink fan includes a heat sink ( 2 ) that is placed on a heat generating electrical component and a fan motor unit ( 4 ) having an axial flow fan ( 18 ) for supplying cooling air to the heat sink ( 2 ). A engaging portions ( 14   a ) of an arm portions ( 14 ) of the fan motor unit ( 4 ) is engaged with a recesses ( 10   b ) of the heat sink ( 2 ). Thus, movement of the fan motor unit ( 4 ) in the axial direction of the heat sink ( 2 ) is restricted so that the fan motor unit ( 4 ) is attached to the heat sink ( 2 ) securely.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a heat sink fan for cooling a microprocessing unit (MPU) or other electrical component and a method formanufacturing a heat sink that is used for the heat sink fan.

2. Description of the Prior Art

A heat sink fan that is attached to an MPU or other heat generatingelectrical component usually includes a heat sink having a plurality ofheat radiating fins that are placed on a MPU and extend radially fromthe central portion. The heat sink fan also includes a fan motor unitthat has an axial flow fan with an impeller, which is surrounded by theheat radiating fins and is disposed at the central portion of the heatsink and at the inner side of the heat radiating fins. The heatradiating fins of the heat sink are cooled by air flow supplied by theaxial flow fan.

One of structures for attaching the fan motor unit to the heat sink isdisclosed in U.S. Pat. No. 6,419,007, for example. In this structure, afan motor unit having a housing made of a synthetic resin is disposedabove the heat sink, and four arm portions are formed at the peripheryportion of the housing. Each of the arm portions extends from thehousing to a base plate that is provided at the lower end of the heatsink so as to cover the outer side of the heat sink. A engaging portionis formed at the tip of the arm portion, and the engaging portion isengaged with an engaged portion formed on the base plate of the heatsink.

Another structure is disclosed in U.S. Pat. No. 5,484,013. In thisstructure, a housing of a fan motor unit is provided with a protrusionconnecting integral to the housing and an arm portion connectingintegral to the periphery of the housing. A pawl portion is provided atthe tip of the arm portion. On the other hand, the heat sink is providedwith a recess for receiving the protrusion of the housing and a flangeportion for receiving the pawl portion of the housing. The protrusion ofthe housing is engaged with the recess of the heat sink, while the pawlportion of the housing is engaged with the flange portion of the heatsink, so that the fan motor unit is attached to the heat sink.

Recently, the amount of heat generated by an MPU has been increasingalong with increase of processing speed and downsizing or larger scaleof integration of the MPU. Therefore, the heat sink fan for cooling theMPU is required to be capable of supplying more cooling air to the heatsink so as to increase cooling efficiency.

However, if a rotation speed of the axial flow fan is increased so as toenhance the cooling efficiency for satisfying the above-mentionedrequirement, the following problem may happen. Namely, theabove-mentioned structure in which four arm portions extend from thehousing to the substrate provided at the lower end of the heat sink hasa disadvantage that when the air flow supplied by the axial flow fanflows along the heat radiating fins and is dissipated outside the heatsink, the arm portions disposed at the outer side of the heat radiatingfins may interrupt the air flow. As a result, the air flow cannot bedissipated sufficiently into the outside of the heat sink, so that thecooling efficiency of the heat sink may be deteriorated. If members suchas the arm portions exist more at the outer side of the heat radiatingfins, or if the area where the members exist is larger, the air flow isinterrupted more so that the cooling efficiency of the heat sink isdeteriorated more. Therefore, it is desirable that there are as littlemembers as possible at the outer side of the heat radiating fins.

In addition, if the arm portions of the housing are extended toward thelower end of the heat sink, a length of the arm portions becomes longer.As a result, the arm portions become easy to generate a distortion suchas warping at the tip of the arm portion when housing is formed by resinmolding. Consequently, it becomes difficult to finish precisely anengaging portion such as the pawl portion at the tip of the arm portion.In this case, it becomes difficult to attach the fan motor unit to theheat sink properly.

Moreover, the heat sink fan is also required to be inexpensive.Therefore, it is necessary to provide the heat sink fan with a simplestructure that enables the fan motor unit to be attached to the heatsink easily and securely.

SUMMARY OF INVENTION

An object of the present invention is to provide a heat sink fan thatcan increase quantity of air flow from an axial flow fan so as toimprove cooling efficiency of a heat sink.

Another object of the present invention is to reduce a number ofcomponents that constitute a structure for attaching a fan motor unithaving the axial flow fan to the heat sink so as to realize a simpleststructure.

Still another object of the present invention is to reduce a cost ofmanufacturing the heat sink fan.

Still another object of the present invention is to attach the fan motorunit to the heat sink more steadily and more securely.

A heat sink fan according to an example of the present inventionincludes a heat sink having a base portion with a central axis and aplurality of heat radiating fins extending away from the central axisand at least one end rim face, and a fan motor unit having an axial flowfan for supplying cooling air to the heat sink and a housing unit forsupporting the axial flow fan.

The housing unit of the fan motor unit include a housing and at leastone arm portions extending to the heat sink, and an engaging portion isformed at a tip of the arm portion. On the other hand, protrusion orrecess that are formed on the envelope surface of the end rim face ofthe heat radiating fins. The engaging portion of the fan motor unit areengaged with the protrusion or recess of the heat sink so that the fanmotor unit is attached to the heat sink.

According to this structure, the fan motor unit can be attached to theheat sink steadily and securely.

In addition, a heat sink according to an example of the presentinvention is manufactured by the following method. First, the heat sinkhaving a base portion with a central axis and a plurality of plate heatradiating fins extending radially in the direction away from the centralaxis is made. Next, protrusion or recess is formed on the envelopesurface of the end rim faces of the heat radiating fins by machiningprocess.

According to this structure, protrusion or recess of the heat sink canbe formed easily and precisely.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a exploded perspective view of a heat sink fan according to afirst embodiment of the present invention.

FIG. 2 is a side view of a heat sink fan illustrated in FIG. 1.

FIG. 3 is a partial enlarged side view showing a method of attaching thefan motor unit to the heat sink illustrated in FIG. 1.

FIG. 4 is a exploded perspective view of a heat sink fan according to asecond embodiment of the present invention.

FIG. 5 is a side view of a heat sink illustrated in FIG. 4.

FIG. 6 is a perspective of a heat sink according to a third embodimentof the present invention.

DETAILED DESCRIPTION

Hereinafter, a heat sink fan and a method for manufacturing a heat sinkthat is used for the heat sink fan in each embodiment of the presentinvention will be explained with reference to FIGS. 1 to 6. Although thevertical direction of the drawing is used as the vertical direction inthe explanation of each embodiment of the present invention, thedirection in the real attachment state is not limited by the explanationor the drawing.

As shown in FIG. 1, a heat sink fan according to the first embodiment ofthe present invention includes a heat sink 2 and a fan motor unit 4 thatis detachably attached to the heat sink 2.

The heat sink 2 is a substantially circular member, which is made ofaluminum, aluminum alloy, copper, copper alloy or other metal havingrelatively high thermal conductivity by an extrusion or other processes.The heat sink 2 includes a column-like base portion 6 having a lower endsurface (6 a in FIG. 2) that is placed on an MPU or other electroniccomponent and a central axis 8 that is perpendicular to the lower endsurface 6 a. The heat sink 2 has a plurality of heat radiating fins 10that are connected integrally to the outer peripheral surface of thebase portion 6 and extending radially away from the central axis. Theheat radiating fins 10 are arranged and distributed equally in thecircumferential direction. Each of the heat radiating fins 10 radiallyextends with a curved shape from the base portion 6. Each end rim faces10 a is formed at the outer end of each of the heat radiating fins 10. Aset of adjoining end rim faces 10 a defines a surface that envelopes thefaces 10 a (hereinafter this surface is referred to as an envelopesurface 11).

Although the base portion and the heat radiating fins are formedintegrally in this embodiment, there can be other structures. Forexample, the heat sink may be made up of a base member and heatradiating fins. In this case, the base member is made of metal havinghigher thermal conductivity such as copper or copper alloy, and the heatradiating fins are made of aluminum, aluminum alloy, copper or copperalloy. The base member is fixed to the heat radiating fins by a pressfitting to make a heat sink. Since the base member having high thermalconductivity is placed directly on the MPU that generates heat, and thecooling efficiency of the heat sink is enhanced. In addition, it ispossible to form two or more end rim faces in each of the heat radiatingfins.

On the other hand, the fan motor unit 4 has a substantially circularhousing 12 that is arrange at the upper side (corresponding to a firstend side) of the heat sink 2 in the axial direction (the upper side inFIGS. 1 and 2). The fan motor unit 4 also has arm portions 14 extendingfrom the housing 12 to the lower side (corresponding to a second endside) in the axial direction (the lower side in FIGS. 1 and 2). Acircular hole 16 is formed in the middle portion of the housing 12 ofthe fan motor unit 4, and a support portions 20 for supporting the axialflow fan 18 is arranged above and around the circular hole 16.

Each support portion 20 includes a support pillar portion 22 around thecircular hole 16 and an extending portion 24 a extending from the upperend of the support pillar portion 22 to the inside toward the centralaxis 8. In this embodiment the fan motor unit 4 has four supportportions 20 and four extending portions 24 a-24 d. The fan motor unit 4also includes a disk portion 26 arranged above the circular hole 16, andfixed to each inner ends of the four extending portions 24 a-24 d. Forsupporting the axial flow fan 18, the upper end of the axial flow fan 18is fixed to the disk portion 26. In this case the disk portion 26 ispositioned above the housing 12 in the axial direction held by thesupport pillar portions 22 and the extending portions 24 a-24 d. Thus,the axial flow fan 18 is also positioned above the housing 12 in theaxial direction. Therefore, the axial flow fan 18 is retained with theentire circumference being exposed out of the fan motor unit 4. Theaxial flow fan 18 inhales an ambient air as a cooling air through theinlet openings defined by the neighboring support pillar portions 22 andone of the extending portions 24 a-24 d, and the air flow is blowntoward the heat sink 2 for cooling the heat sink 2. Furthermore, theaxial flow fan 18 can be detachably attached to the disk portion 26. Theheat sink fan of the present invention can be used semi-permanently byreplacing the worn axial flow fan 18 with a new one.

In addition, the extending portion 24 b is provided with a guide groove24 b 1 opening upward over the entire length of the extending portion 24b. This guide groove 24 b 1 is used for leading out electric wires 30that connect the axial flow fan 18 with an external power sourceelectrically.

In addition, the housing 12 is provided with a pair of positioningportions 28 formed at the opposing two positions on the outercircumference of the housing 12, and a pair of arm portions 14 formed atother opposing two positions on the outer circumference of the housing12. Wherein these positions has the relation that an imaginary line (notshown on FIG. 1) connecting the two positions of the positioningportions 28 is perpendicular to another imaginary line (also not shownon FIG. 1) connecting the positions of the arm portions 14. Thepositioning portions 28 extend from the housing 12 downward and contactthe envelope surface 11 of the heat radiating fins 10. The pair of armportions 14 and 14 and the pair of positioning portions 28 and 28prevent the housing 4 securely from moving or sliding away from thecenter position of the heat sink 2 in the radial direction. Although thepair of positioning portions 28 and 28 are provided in this embodiment,they can be provided more or only one.

In addition, there are two portions 10 c having flat envelope surfaceson the envelope surface 11 on which recesses 10 b are formed as beingexplained later. The flat envelope portions 10 c is formed in parallelto the central axis 8. In addition, the flat envelope portions 10 c isformed by cutting the end of corresponding heat radiating fins 10 sothat the length of them that is extending radially away from the centralaxis 8 become shorter than other heat radiating fins 10. When the fanmotor unit is set on the heat sink 2, the inner surfaces of thepositioning portions 28 are closely contacted with the flat envelopportions 10 c. Thus, only a slight movement or a slight slide of the fanmotor unit 4 on the heat sink 2 in the radial direction can beprevented. A plurality of the flat envelop portions 10 c can be formedon the envelope surface 11 of the heat sink 2. For example, the flatenvelop portion may be formed on the envelope surface 11 of the heatsink 2 at the position opposing the positioning portions 28 of the fanmotor unit 4. Thus, the area where the positioning portions 28 contactsthe envelope surface 11 can be increased, so that the effect ofpreventing the fan motor unit 4 from moving on the heat sink 2 from ortoward the central axis 8 can be enhanced.

As a material of the housing 12, an engineering plastic resin or othermaterial having a heat-resistant property, a small coefficient ofthermal expansion and a good dimensional stability is preferable.Especially, saturated polyester is preferable since it is easy to workor make forming. More specifically, polybutylene terephthalate (PBT) orpolyethylen terephthalate (PET) reinforced with glass fibers issuitable. Content of the glass fiber can be determined in accordancewith a mechanical strength or a dimension stability that is required.Usually, it is preferable that the content of the glass fiber be withina range of 10-40 weight percent, particularly 25-35 weight percent. Amethod for making the housing 12 using the above-mentioned material isnot limited but can be a conventional method such as an injectionmolding.

Next, features of the present invention will be explained in detail withreference to FIGS. 1-3. FIG. 3 is a partial enlarged side view showing amethod of attaching the fan motor unit 4 to the heat sink 2 illustratedin FIG. 1.

As shown in FIGS. 2 and 3, recesses 10 b are concave portions in theradial direction getting close to the central axis 8, and are formed onthe envelope surface 11 of the heat sink 2. The recesses 10 b are formedby machining the envelope surface 11 by using a cutting tool afterforming the base portion 6 and the heat radiating fins 10 by anextrusion process.

On the other hand, an engaging portion 14 a is formed at the tip of eachof arm portions 14 of the housing 12. The engaging portion 14 a has apawl-like shape with a flat surface 14 a 1 extending from the tipportion of the arm portions 14 toward the central axis 8.

As shown in FIG. 1, in order to attach the fan motor unit 4 to the heatsink 2, the arm portions 14 of the fan motor unit 4 are positioned abovethe recesses 10 b of the heat sink 2 in the axial direction, and the fanmotor unit 4 is moved downward in the axial direction of the heat sink2. As shown in FIG. 3, the engaging portions 14 a of the arm portions 14of the fan motor unit 4 contact the end rim faces 10 a of the heat sink2 and are expanded a little in the radial direction away from thecentral axis 8 by an elastic deformation. When the engaging portions 14a reach the recesses 10 b of the heat sink 2, the engaging portions 14 afit in the recesses 10 b by the elastic restoring force of the armportions 14. On this occasion, the flat surfaces 14 a 1 of the engagingportions 14 a engage the upper end wall surfaces of the recesses 10 b,where each end wall surface is formed as an envelope surface whichenvelopes lower end faces cut so as to make the recess 10 b of thecorresponding fins 10. As a result, movement of the fan motor unit 4 isrestricted in the axial direction, so that the fan motor unit 4 isattached to heat sink 2 securely. In order to detach the heat sink 2from the fan motor unit 4, the engaging portions 14 a are pressedoutward slightly away from the central axis 8 first so that theengagements between the recesses 10 b of the heat sink 2 and theengaging portions 14 a are released. Then, the fan motor unit 4 is movedupward from the heat sink 2 in the axial direction. In this way, the fanmotor unit 4 can be detached from the heat sink 2. Thus, the fan motorunit 4 is detachably attached to the heat sink 2.

Furthermore, the shape of the engaging portions 14 a of the fan motorunit 4 is not limited to the pawl-like shape but various conventionalshapes can be adopted. For example, a hook shape is also possiblyadopted as the shape of the engaging portions. In addition, although twoarm portions 14 and two engaging portions 14 a and two recesses 10 b areprovided as shown in FIGS. 1 and 2, it is possible to provide only oneor more than two for each of the arm portions 14 and engaging portions14 a and recesses 10 b.

When the axial flow fan 18 is turned in a predetermined direction in theheat sink fan of this embodiment (in the clockwise direction in thisembodiment), the ambient air as the cooling air is inhaled through thecircular hole 16 of the fan motor unit 4, and the air flow is blowntoward the heat sink 2 and flows along the heat radiating fins 10. Onthe other hand, heat generated by the MPU or other electrical componentis conducted to the plural heat radiating fins 10 via the lower endsurface 6 a of the base portion 6 of the heat sink 2. Then, the air flowsupplied from the axial flow fan 18 flows along the heat radiating fins10 when the heat is transferred from the heat radiating fins 10 to theair flow. Thus, the heat generated by the electrical component istransferred from the heat sink 2 to the air flow and is dissipated bythe air flow into the outside of the heat sink 2.

The axial flow fan 18 is positioned above the heat sink 2 so as toprotrude from the housing 12 in the axial direction in this embodiment.Thus, the axial flow fan 18 can inhale ambient air as much as possiblewhen the axial flow fan 18 rotates at a high speed. As a result, theaxial flow fan 18 can blow much air flow toward the heat sink 2 so thatcooling efficiency of the heat sink 2 can be improved.

In addition, the axial flow fan 18 generates a spiral air flow, and theheat radiating fins 10 arranged radially can receive the air flowefficiently so that the cooling efficiency of the heat sink 2 can beimproved.

Conventionally, an axial flow fan is housed in a heat sink. In contrast,the axial flow fan is positioned above the heat sink in the axialdirection in the present invention, so that heat radiating fins and abase portion can be arranged in the space where the axial flow fan wasarranged conventionally in the heat sink. As a result, a heat radiatingarea of the heat sink 2 can be increased so that the cooling efficiencyof the heat sink 2 can be further improved.

In addition, the recesses 10 b are provided to the envelope surface 11of the heat sink 2, while the engaging portions 14 a are provided to thetip of the arm portions 14 of the fan motor unit 4 in the presentinvention. According to this structure, the fan motor unit 4 can beattached to the heat sink 2 securely with sufficient fixing strength bya simple structure without increasing members for the attachment.Moreover, a cost for manufacturing the heat sink fan can be reduced.

In addition, since the recesses 10 b are provided to the envelopesurface 11 of the heat sink 2, a length of the arm portions 14 extendingdownward in the axial direction from the housing 12 can be shortened.Thus, the section area of the arm portions 14 can be minimized. Namely,the areas of the arm portions 14 can be decreased to the extent thatdoes not affect substantially the cooling efficiency of the heat sink 2.Accordingly, it is prevented that the arm portions 14 of the fan motorunit 4 interrupt the air flow when the air flow supplied from the axialflow fan 18 flows along the heat radiating fins 10 and dissipated intothe outside of the heat sink 2. In addition, since the length of the armportions 14 extending downward from the housing 12 in the axialdirection can be shortened, distortion such as a warpage that can begenerated easily when the housing 12 of the arm portions 14 is formed byresin molding can be prevented, so that the arm portions 14 can beformed with high accuracy.

In addition, the recesses 10 b can be formed by a machining processusing a cutting tool after the base portion 6 and the heat radiatingfins 10 are formed by extrusion or other process. Accordingly, therecessed 10 b can be formed by a simple process.

In addition, flexibility in designing the portion where the recesses 10b is formed can be increased. Namely, fastening strength between the fanmotor unit 4 and the heat sink 2 on the envelope surface 11 can beincreased, and the recesses 10 b can be formed easily at the positionthat does not affect substantially the cooling efficiency of the heatsink 2, i.e., the position a little above from the middle of the heatsink 2 in the axial direction.

In addition, the heat radiating fins 10 of the heat sink 2 extendradially away from the central axis 8 a explained above, and the heatradiating fins 10 are formed in the shape curving in the oppositedirection (counterclockwise direction) to the rotation direction of theaxial flow fan 18 in this embodiment. Conventionally, there is a casewhere the air flow from the axial flow fan 18 cannot be blownefficiently to the base portion 6 that become the highest temperature inthe heat sink 2 in the structure where the heat sink 2 is relativelyclose to the axial flow fan 18. However, if the heat radiating finsshape of this embodiment is used, the air flow from the axial flow fan18 can be blown to the base portion 6 efficiently along the curved heatradiating fins 10. As a result, the cooling efficiency of the heat sink2 becomes higher than the conventional structure. It is possible to makea shape of the heat radiating fins so as to extend slanting in apredetermined direction with respect to the central axis, and thisstructure can acquire the same effect as the present invention.

Next, a second embodiment of the present invention will be explained indetail with reference to FIGS. 4 and 5. The heat sink fan of thisembodiment has the basic structure that is the same as the firstembodiment, and each reference number used for each correspondingelement is increased by 100. The explanation of the second embodimentwill be described mainly about different portions from the firstembodiment.

There are provided protrusions 110 c on the envelope surface 111 of theheat sink 102. The protrusions 110 c are protrusive portions in theradial direction away from the central axis 108, and are formed bycutting the upper portion and the lower portion of the envelope surface111 using a cutting tool in a machining process after forming the baseportion 106 and the heat radiating fins 110 by extrusion or otherprocess. In this way, notch portions 115 a and 115 b having asubstantially L-shape in a side view are formed on the envelope surface111 at the upper portion and the lower portion of the protrusion 110 cin the axial direction. Namely, the protrusion 110 c is formed as shownin FIG. 5.

The fan motor unit 104 has the same structure as the first embodiment.

As shown in FIG. 4, in order to attach the fan motor unit 104 to theheat sink 102, the arm portions 114 of the fan motor unit 104 arepositioned above the protrusions 110 c of the heat sink 102 in the axialdirection, and the fan motor unit 104 is moved downward in the axialdirection of the heat sink 102. The engaging portions 114 a of the armportions 114 of the fan motor unit 104 contact the protrusions 110 c ofthe heat sink 102 first, and the arm portions 114 are expanded a littlein the radial direction away from the central axis 108 by an elasticdeformation. When the engaging portions 114 a reach the notch portions115 b of the heat sink 102, the engaging portions 114 a fit in the notchportions 115 b by the elastic restoring force of the arm portions 114.On this occasion, a flat surfaces 114 a 1 of the engaging portions 114 acontact the upper end surface of the protrusions 110 c. As a result,movement of the fan motor unit 104 in the axial direction is restricted,so that the fan motor unit 104 is attached to the heat sink 102securely. In order to detach the fan motor unit 104 from the heat sink102, the engaging portions 114 a are pressed outward slightly away fromthe central axis 108 first so that the engagements between theprotrusions 110 c of the heat sink 2 and the engaging portions 114 a arereleased. Then, the fan motor unit 104 is moved upward from the heatsink 102 in the axial direction. Thus, the fan motor unit 104 can bedetached from the heat sink 102. In this way, the fan motor unit 104 isdetachably attached to the heat sink 102.

Furthermore, although the protrusions is provided to the heat sink,while the engaging portions is provided to the fan motor unit in thisembodiment, other structure can be adopted. For example, it is possiblethat the protrusions is formed on the envelope surface of the heat sinkand the engaging portions of fan motor unit is formed as a recesses.Moreover, the shape of the engaging portions 114 a of the fan motor unit104 is not limited to the pawl-like shape but various conventionalshapes can be adopted. In addition, although two arm portions 114, twoengaging portions 114 a and two protrusions are provided as shown inFIGS. 4 and 5, it is possible to provide only one or more than two foreach pair of the arm portions 114, engaging portions 114 a andprotrusions.

Thus, this embodiment can also acquire the same effect as the firstembodiment.

Next, a third embodiment of the present invention will be explained indetail with reference to FIG. 6. The heat sink 52 of this embodiment hasa substantially rectangular shape, which is made of aluminum, aluminumalloy, copper, copper alloy or other material having high thermalconductivity by extrusion or other process. The heat sink 52 has a lowerend surface that is placed on an MPU or other electrical component and asubstantially rectangular base portion 56 with a central axis 58 that isperpendicular to the lower end surface. In addition, the heat sink 52has leg portions 56 d that are formed integrally to the outer peripheryof the base portion 56 and extend from edge portions on the outerperiphery of the base portion 56 outward in the direction away from thecentral axis 58. The heat sink 52 also has a plurality of heat radiatingfins 60 that extend from the base portion 56 and the leg portions 56 din the direction away from the central axis 58. Each of the heatradiating fins 60 has an end rim faces 60 a at the outer end. There isformed a surface that envelopes the plural end rim faces 60 a of theheat radiating fins 60 (hereinafter this surface is referred to as anenvelope surface 61).

Although the base portion 56 and the heat radiating fins 60 are formedas one unit this embodiment, other structures can also be adopted. Forexample, the heat sink may be made up of a base member and heatradiating fins. Namely, it is possible to use copper or a copper alloyhaving higher thermal conductivity for making the base member and to usealuminum, an aluminum alloy, copper or a copper alloy for making theheat radiating fins using. The base member is fixed to the heatradiating fins by a press fitting process to make a heat sink. Since thebase member having high thermal conductivity is placed directly on theMPU that generates heat, cooling efficiency of the heat sink is furtherenhanced.

In addition, recesses 60 b are formed on the envelope surface 61 of theheat radiating fins 60 at the area that include plural neighboring heatradiating fins 60. The recesses 60 b are formed by a machining processusing a cutting tool after forming the base portion 56 and the heatradiating fins 60 by extrusion or other processes.

On the other hand, the fan motor unit is formed in the same way as thefirst embodiment of the present invention, and only the outer shape ofthe housing is formed in a substantially rectangular shape.

Even if the outer shape of the heat sink is different, the fan motorunit can be attached to the heat sink 52 securely in the same way as thefirst embodiment in this embodiment.

It is possible to provide only one or more than two the recesses 60 b.It is also possible to replace with recesses 60 b and to provideprotrusions in the envelope surface 61.

Next, a method for manufacturing the heat sink of the present inventionwill be explained in detail.

First, a metal material such as aluminum, aluminum alloy having highthermal conductivity is heated up to a predetermined temperature. A dieis prepared that has a bore of the same shape as the cross section ofthe heat sink of the present invention. Then, the above-mentioned metalmaterial held in an extrusion machine is forced to pass through the boreof the die in the extrusion direction. In this way, the heat sink havingthe base portion and the plurality of radial heat radiating fins isformed. Next, using a cutting tool, a machining process is applied tothe envelope surface of the heat sink after the extrusion formation sothat protrusions or recesses are formed.

A method for manufacturing the heat sink including the base member andthe plurality of heat radiating fins will be explained in detail. First,the column-like base member is formed. Then, using the above-mentionedextrusion method, the heat sink having the plurality of radial heatradiating fins and a central hole arranged in the center of the heatradiating fins is formed. Then, as explained above, a machining processis applied to the envelope surface of the heat sink after the extrusionformation using a cutting tool so that protrusions or recesses areformed. Finally, the base member is pressed to fit in the central holeof the heat radiating fins and is fixed to the heat sink.

Thus, the protrusions or the recesses can be formed easily and correctlyon the heat sink. Therefore, a heat sink having a good coolingefficiency can be realized in a low cost.

Though embodiments of the heat sink fan and the method for producing theheat sink that is used for the heat sink fan according to the presentinvention are explained above, the present invention should beunderstood as not being limited to the embodiment. Various modificationscan be possible within the scope of the present invention.

For example, although the heat sink is formed by extrusion in eachembodiment, other processes such as a drawing process or a cuttingprocess can be used for forming a desired shape of the heat sink.

1. A heat sink fan for cooling a heat generating electrical component,comprising: a heat sink including a base portion with a central axis anda plurality of heat radiating fins integrally or fixedly formed on theside surface of the base portion, each of the heat radiating finsextending away from the central axis, and having at least one end rimface; a fan motor unit including an axial flow fan having a rotationalaxis, a housing unit connected fixedly with the axial flow fan, thehousing unit having a housing and at least one arm portion, wherein thefan motor unit is arranged by the housing unit where the rotational axisis substantially corresponding to the central axis on a first end of theheat sink, for supplying cooling air to the heat sink, the arm portionis extending from the housing to a second end side of the heat sink, andan engaging portion is formed at a tip of the arm portion; and aprotrusion or a recess formed on an envelope surface of the end rimfaces of the heat radiating fins, wherein the engaging portion isengaged with the protrusion or the recess so that the fan motor unit isattached to the heat sink with restriction of relative movement in theaxial direction.
 2. The heat sink fan according to claim 1, wherein theprotrusion or the recess is formed by a machining process of theenvelope surface after forming the base portion and the heat radiatingfins.
 3. The heat sink fan according to claim 1, the fan motor unitadditionally having at least one positioning portion extending from thehousing to the second end side of the heat sink, wherein an innersurface of the positioning portion is contacted with a part of anenvelope surface of the heat radiating fins, for preventing the fanmotor unit from moving against the heat sink radially.
 4. The heat sinkfan according to claim 1, wherein at least one flat envelope portion isformed on the envelope surface of the heat radiating fins, the flatenvelope portion being parallel to the central axis and formed bycontrolling lengths of a portion of the heat radiating fins indirections away from the central axis.
 5. The heat sink fan according toclaim 1, wherein the heat radiating fins extend radially with beingcurved in a predetermined direction with respect to the central axis. 6.The heat sink fan according to claim 1, wherein the heat radiating finsextend radially with being slanted in a predetermined direction withrespect to the central axis.
 7. The heat sink fan according to claim 1,wherein the engaging portion is formed like a pawl or a hook extendingfrom the tip of the arm portion toward the central axis.
 8. The heatsink fan according to claim 1, wherein two or more the arm potions isextending from the housing to a second end side of the heat sink.
 9. Theheat sink fan according to claim 8, wherein two or more the positioningportion is extending from the housing to the second end side of the heatsink.
 10. A heat sink fan for cooling a heat generating electricalcomponent, comprising: a heat sink including a base portion with acentral axis and a plurality of heat radiating fins integrally orfixedly formed on the side surface of the base portion, each of the heatradiating fins extending away from the central axis, and having at leastone end rim face; a fan motor unit including an axial flow fan having arotational axis, a housing unit connected fixedly with the axial flowfan, the housing unit having a housing and two or more arm portions,wherein the fan motor unit is arranged by the housing unit where therotational axis is substantially corresponding to the central axis on afirst end of the heat sink, for supplying cooling air to the heat sink,the arm portions is extending from the housing to a second end side ofthe heat sink, and two or more engaging portions is formed at a tip ofthe arm portions; and two or more protrusions or recesses formed on anenvelope surface of the end rim faces of the heat radiating fins,wherein the engaging portions is engaged with the protrusions or therecesses so that the fan motor unit is attached to the heat sink withrestriction of relative movement in the axial direction.
 11. The heatsink fan according to claim 10, wherein the fan motor unit additionallyhaving at least one positioning portion extending from the housing tothe second end side of the heat sink, wherein a inner surface of thepositioning portion is contacted with a part of an envelope surface ofthe heat radiating fins, for preventing the fan motor unit from movingagainst the heat sink radially.
 12. The heat sink fan according to claim10, wherein the fan motor unit additionally having two or morepositioning portions extending from the housing to the second end sideof the heat sink, wherein a inner surface of the positioning portionsare contacted with a part of an envelope surface of the heat radiatingfins, for preventing the fan motor unit from moving against the heatsink radially.
 13. A method for manufacturing a heat sink that is placedon a heat generating electrical component, the method comprising thesteps of: forming a heat sink that includes a base portion with acentral axis and a plurality of heat radiating fins integrally orfixedly formed on the side surface of the base portion, each of the heatradiating fins extending from the central axis, and having at least oneend rim face; and forming a protrusion or a recess on an envelopesurface of the end rim faces of the heat sink by a machining process.14. A method for manufacturing a heat sink that is placed on a heatgenerating electrical component, the method comprising the steps of:forming a base member having a central axis; forming a heat sinkincluding a plurality of plate-like heat radiating fins integrally orfixedly formed on the side surface of the base portion, each of the heatradiating fins extending from the central axis, and having at least oneend rim face, and a central hole arranged in the center of the heatradiating fins; forming a protrusion or a recess on an envelope surfaceof the end rim faces of the heat sink by a machining process; andpressing the base member to fit in the central hole of the heat sink andto be fixed to the heat sink.